Compound dip process for metal cans

ABSTRACT

Sealant is applied onto or into a folded-seam closure of a metal can. Instead of introducing sealant into the U-shaped lid flange and drying, the compound or sealant is applied to the base flange. The base of the metal can is dipped into a current of fluid sealant or atl least brought into contact with it at the surface. This substantially imnproves the precision of dosing and the exact amount of applied sealant.

[0001] The technical field of the invention is a process for anapplication of sealant (so-called “compound”) to a body hook of a bodyof a metal can.

[0002] Prior art realizes sealings on metal packings such that asealant, which is usually provided on the basis of a rubber preparationor a synthetic caoutchouc, is dispersed in water or organic solvents(SBC or WBC) and introduced into the end hook of a can end or into thefold edge of a can base with a spraying gun. Subsequently, the water orthe solvent (mixture) has to be evaporated and the dried seal has to bestored at least 24 hours before closing the can end and the can body(compare DE-A 27 27 628 or U.S. Pat. No. 4,201,308). In the prior artprocess, the quantity of sealant used is subject to a statisticalvariation, the effectively introduced or applied sealant depending to aconsiderable degree on the viscosity, which in turn depends on thetemperature. Consequently, the temperature determines the quantity ofsealant introduced, namely the circumferential distribution of sealantas well as the thickness of the sealant introduced.

[0003] It is an object of the present invention to improve the processesfor introduction or application of sealant previously used, particularlywith regard to their precision and reproducibility. The objective is tomake the quantity of sealant applied or introduced independent onexternal influences to such a degree that it may be positioned moreprecisely to permit on a long-term basis the saving of considerablequantities of sealant.

[0004] Said object is achieved by applying a sealant to the body hook ofa can body (claim 1), and not to a can end, said application beingeffected before flanging the seam, which particularly is a double seam.

[0005] By realizing the inventive idea, a frequent control of thesealant is not required, the can body itself being dipped from aboveinto the sealant or contacting it to such a degree that only therequired portion of the body hook is wetted with said sealant. Comparedto prior art, the inventive process permits a better positioning andtherefore, a more precise application and consequently a moreeconomizing dosing of the sealant. Thus a considerable quantity ofsealant is saved over a fairly long time. Due to the invention, defectsin the rubber-coating of can ends are a thing of the past.

[0006] To fluidize the raw sealant, it is softened (fluidized), usuallyby an extruder or compounder. The compound may then be transferred on agravure roller (claim 3) which may be supplied by a sheet die (claim 4),however, said sheet die itself also being able to provide the fluidalcompound without using a deep-draw roller¹, said compound presenting acertain minimum dipping depth; said minimum depth may be controlled(claim 3).

[0007] Also, time, speed and dipping depth of the dipping movement ofthe body hook may be controlled (claim 2, 7).

[0008] The application of compound on the seam portion of the can body(body hook) is improved with regard to uniformity by rotating said canbody in the indicated direction α, (alpha) around its own axis at leastwhen it contacts or is dipped into the sealant. For this purpose, amagnetic drive (for soft metal² cans) may be provided.

[0009] By combining a dipping movement in vertically downward directionand a rotatory movement around the axis, a high degree of uniformity ofsealant on the body hook is achieved, simultaneously permitting aprecise positionning and dosing and thus savings of largest possiblequantities of sealant to achieve smallest necessary quantities ofsealant on the body hook.

[0010] In the following, the invention is described more in detail onthe basis of embodiments.

[0011]FIG. 1 illustrates a closed double seam being provided on theupper edge of a metal packing. D designates the double seam, referencenumeral 1 designates the body of the metal can and reference numeral 2designates the can end.

[0012]FIG. 2 shows the dipping movement in downward direction of aschematically illustrated can body 1 into a fluidal sealant 10 beingcontinuously replenished in y direction (“stream of sealant”).

[0013]FIG. 3 is an enlarged view of the edge portion of a seam portion 1a of a can body, onto which a defined, precisely dosed quantity 10 a ofa sealant has been applied according to the process of FIG. 2.

[0014]FIG. 4,

[0015]FIG. 5 show embodiments of usual seam geometries on metal cans.

[0016] If a can is in closed condition, an end hook 2 a,2 b is seamedtogether with a body hook 1 a to provide an air-tight double seam D. Asealant C is provided on the upper portion of the seam portion, betweenthe seam portion 1 a of the can body and the outer seam portion 2 b ofthe can end portion 2 a,2 b, and, possibly, a further sealant F isprovided on the lower portion of said seam.

[0017]FIGS. 2 and 3 illustrate the application of at least one of saidsealants C and F.

[0018]FIG. 2 illustrates the principle, according to which a can body 1,being shown schematically, is dipped into a fluidal sealant 10 (“rawsealant”). Said can body 1 is moved downward v in direction of the canaxis 100 until the body hook 1 a contacts said fluidal compound 10. Saidmovement v may as well be continued a bit further downward, so that thelower (reverse) surface of said body hook 1 a is also dipped.

[0019] The dipping depth may exceed the thickness d of the metal sheetso that said compound 10 also reaches the reverse side (upper side) ofsaid body hook 1 a, thus providing a sealing portion F when the can isclosed.

[0020]FIG. 2 is an exaggerated illustration showing a (frustoconical)inclination of said body hook 1 a, said inclination being substantiallyhorizontal with an only slight inclination, such as shown in FIGS. 4 and5.

[0021] In FIG. 2, the downward movement is designated by a velocity vwhich is changed depending on the position of said can body 1 and theinterspace between said can body 1 and said compound 10. The smaller theinterspace between said body 1 and said fluid 10, the lower the velocityof said downward movement.

[0022] During said downward movement or immediately when contacting orbeing dipped into said fluidal compound 10, said body 1 may rotatearound the can axis 100, thus improving the uniformity of application ofsaid compound.

[0023] A movement y of said fluid 10 is schematically illustrated,representing a slight movement of said fluid or at least a continuousreplacement of fluid in a quantity corresponding to the quantity ofsealant being applied to said body hooks 1 a which are dipped into orbrought in contact with said sealant. Said fluidal compound 10 may beproduced by an extruder, its temperature may be controlled to maintainits viscosity on a substantially constant level.

[0024]FIG. 3 illustrates a sealant 10 a being positioned on said bodyhook 1 a in an exactly dosed quantity. Said Figure only shows an edgeportion 1 a of said can body 1 being illustrated in upright positionwith its base downwards. If, after dipping and removing said body, saidcompound 10 still presents a certain mobility or viscosity, saidcompound 10 a is still able to slightly move in radially inwarddirection on the can end seam 1 a after quickly reversing said can 1.

[0025] Said movement in radially inward and downward direction dependson the ambient temperature and the inclination of said body hook 1 awith regard to the horizontal plane.

[0026] If the body hook 1 a is dipped somewhat more deeply into saidfluid 10, a bilateral coating 10 b with compound is provided around theouter edge 1 b of said body hook 1 a, thus forming a lower sealingportion F when seaming. Said compound portions C and F according to FIG.1 are indicated in FIG. 3.

[0027] Said process of application may equally be used in the can endand base seam of three-piece cans (see FIG. 4). Its use is also possiblewith stretched one-piece can bodies, their upper portion drawn-in or not(see FIG. 5).

[0028]FIG. 4 and FIG. 5 comprise usual seam dimension and their usualreference numerals.

1. Process for an application or introduction of a sealant (10;“compound”) between (C,F) an end hook (2 a,2 b) and a body hook (1 a) ofa seam (D) between an end (2) and a body (1) of a metal packing, wherebysaid compound (10;10 a, 10 b) is applied (v,α,y) to said body hook (1 a)before applying said end (2) and closing said end hook (2 a,2 b) andsaid body hook (1 a).
 2. Process according to claim 1, wherein the bodyhook (1 a) of said can body (1) is dipped from above into a fluidalcompound (10) or brought into contact (v) with a fluidal compound. 3.Process according to claims 1 or 2, wherein the maximum possible dippingdepth (t) of the raw compound (10) for the end hook (1 a) is controlledby a roller.
 4. Process according to one of the claims 1 to 3, whereinsaid raw compound (10) is provided via a sheet die for application onthe body hook (1 a).
 5. Process according to one of the aforementionedclaims, wherein said body (1) and said body hook (1 a) are rotated (α)at least when contacting or being dipped into said raw compound (10). 6.Process according to one of the aforementioned claims, wherein theapplication of the compound (10) is effected by a downward movement (v)and a rotatory movement (α) of said can body (1).
 7. Process accordingto one of the aforementioned claims, wherein the dipping depth of saidbody hook (1 a) is slightly deeper than the thickness (d) of the metalsheet to apply (10 b) said compound (10) also on the reverse side ofsaid body hook (1 a).
 8. Process according to claim 7, wherein saidfluidal compound is applied onto and around the outer edge (1 b) of saidbody hook by dipping.
 9. Process according to one of the aforementionedclaims, wherein said seam is a multiple seam, particularly a doubleseam.
 10. Process according to one of the aforementioned claims, whereinat least one of the radial position and the distribution of the appliedcompound being modified, particularly slightly in radially inwarddirection, by quickly reversing said can body (1) after dipping into orcontact with said compound.
 1. Process for an application orintroduction of a sealant (10; “compound”) between (C,F) an end hook (2a,2 b) and a body hook (1 a) of a seam (D) between a metal end (2) and ametal body (1) of a metal packing, whereby said compound (10;10 a,10 b)is applied (v,α,y) before applying said end (2) and closing said endhook (2 a,2 b) and said body hook (1 a), characterized in that saidcompound (10) being applied to said body hook (1 a) by dipping the bodyhook (1 a) of said can body (1) from above into a fluidal compound (10)or by bringing said body hook (1 a) into contact (v) with a fluidalcompound.
 2. Process according to claim 1, wherein at least one of theradial position and the distribution of the applied compound beingmodified by quickly reversing said can body (1) after dipping into orcontacting said compound, said modification being directed particularlyslightly radially inward.
 3. Process according to claims 1 or 2, whereinat least one of the dipping depth (t) of said body hook (1 a) into saidcompound (10) and the minimum depth of said fluidal compound (10) beingcontrolled.
 4. Process according to one of the claims 1 to 3, whereinsaid compound (10) is provided via a sheet die for application on saidbody hook (1 a).
 5. Process according to one of the aforementionedclaims, wherein said body (1) and said body hook (1 a) are rotated(α,alpha) at least when contacting or being dipped into said compound(10).
 6. Process according to one of the aforementioned claims, whereinthe application of said compound (10) is effected by a downward movement(v) and a rotatory movement (α,alpha) of said can body (1).
 7. Processaccording to one of the aforementioned claims, wherein the dipping depthof said body hook (1 a) is slightly deeper than the thickness (d) of themetal sheet to apply (10 b) said compound (10) also on the reverse sideof said body hook (1 a).
 8. Process according to claim 7, wherein saidfluidal compound is applied onto and around the outer edge (1 b) of saidbody hook by dipping.
 9. Process according to one of the aforementionedclaims, wherein said seam is a multiple seam, particularly a doubleseam.